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Testing magnetos during engine failure
I'm a student pilot (PPL) and the C172 I fly has the following item in the emergency checklist for in-flight engine failures:
MAGNETOS...............TEST

My instructor has taught me the memory item verbatim as: "Fly on best magneto".
What does this mean exactly? Why fly on "best" magneto? In my mind, selecting BOTH is still using the "best" one, even if the other one failed.
In which situation would selecting magneto LEFT or RIGHT, rather than BOTH, be favorable during an engine malfunction or failure, mid-flight?

If you have a mag failure, it may just quit and act like it's not there, but it can also do things that will make the engine feel like it wants to leave the airplane and move to another city. That is, really rough running.
If a mag just quits working completely while in cruise, chances are, unless you are paying really careful attention at the time, you won't even notice it, and the surprise will come at the next runup.
The typical in-flight failure you WILL notice is sudden banging and vibration that makes you jump out of your skin. As one example, a traditional mag has an internal plastic timing gear driving the distributor. If the teeth are worn down, the gear might skip a bunch of teeth, advancing the timing way out of specification although it still may still fire the plugs, and you'll feel it in the cockpit.
Severely advanced timing will likely be damaging cylinders, so you want that magneto off now.
You aren't going to have a simultaneous double magnetor failure, where everything goes quiet due to lack of ignition, in any normal universe; the statistical probability is too close to zero (unless the plane has one of those single-drive dual bendix mags and the drive fails).
What's going to happen is one will quietly stop working (like a coil failure), which likely result in you carrying on unawares, or you might start to notice a subtle skipping as one mag misfires randomly (internal capacitor failures can do that), or, it will fail in an active manner that results in crazy roughness, like a major timing shift as I described.
You want to disable the bad mag ASAP, so you immediately select the individual mags to identify the bad one, and carry on with the ignition switch selected to the good one.
And if the roughness was actually caused by something else, you've confirmed the mags are not the problem, and carry on with them at BOTH.

A tip I've been using lately.  As part of shutting down, I now always do a P-wire check, and thus I'll discover if I had been flying on a failed mag prior to my next runup.  When I switched from renter to owner, it became MY head/body being in the propellor path to get the tug/towbar onto the lugs, and not the line crew's.  It makes one go "gee, I think I better learn about magneto grounding!"

The live mag check is a basic part of flight training really.  I also do a mag check during the climb at altitude, especially if departing on a long trip, because the stress level is higher and a problem will show up, that won't on a run-up, that could catch you while you're away.  Just a quick flip L, R, listening to the engine, back to both.

I am almost annually disappointed by something I learn that I should have been taught 30+ years ago!  I flew for decades before I found out that the screwdriver bit at the end of the usual fuel drain tool was reversible between slot and philips!!!  The P-Wire test was probably one of those things.  My other mag question is, why are Cessna Mags Both-R-L on the keyhole, and not Both-L-R?

No idea why they do it that way.  Shouldn't really make any difference.  When you are at START, only one mag is energized, normally the left one, which has the impulse coupling.  But I don't see how that could affect the LR pairing.

Each of the cylinders in the engine has two spark plugs, one connected to each magneto.
If one spark plug is fouled or fails, the combustion in that cylinder will not be as complete as it is in the other cylinders that have two working spark plugs.  This imbalance of power produced means the engine will run roughly, or potentially even not run at all.
So, you’re not running on the best magneto per se, but on the magneto that is connected to the best spark plugs.  That means the engine will run more smoothly because all cylinders are producing the same (albeit slightly reduced) power.

This explains how and why to get a rough engine to run more smoothly, but the question was about engine failure.  @Chris, how does this answer your question?

@MichaelHall well it answers my question partly because engine malfunction is part of it I guess, but you are right.

I suggest you clarify this with your instructor.  If your engine fully quits then simply switching mags won’t help.

@MichaelHall my guess is that the "engine failure" checklist serves as a catch-all "engine issues" checklist.


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Apply back-pressure during taxi?
My CFI (PPL) has on a few occasions pointed out that I need to apply back-pressure during taxi, even if we're taxiing on the apron at ~5 knots.
While I can understand the benefits of doing so during takeoff rolls and expedient backtracks, surely the effects of applying back-pressure on anything below 10-15 knots must be negligible?
I fly a C172 and I've heard that they have notoriously sensitive nose wheels, but still.
Am I misunderstanding something or is my CFI just trying to make me develop good habits (for when rolling faster)?

@757toga I did ask him if it mattered during slow speeds and he agreed that the effect isn't much although not negligible. He then mentioned something about reducing the risk of a prop strike, which I didn't understand at the time (for the same reasons explained in my post). In retrospect, his explanation now sounds very much like what GdD said below.

Back pressure is not negligible at taxi speeds, the prop is still running and even at idle will give you some elevator authority. While it's not that much with the elevator fully back you will lift the nose a bit, and if you hit a rut that can make the difference between getting over it or having prop strike.
The ground handling of a c172 is also better with a bit of weight off the nose.

I see. So the elevator authority is almost entirely due to the prop wash, correct?

At taxi speeds that's correct @Chris. You can feel the difference, next time hold the brakes and keep the RPM at 1200, then pull the yoke back to your lap and the nose will lift a bit.

Thanks. Would be interesting to one day test pulling back with full power and with the breaks applied. I suppose it would be visibly noticeable on the nose wheel suspension. Just a thought. Edit: Saw your edit after I posted this.

Tell your CFI you want to try that, I can't see why they'd say no. Maybe at power check RPM not full throttle.

I recall a true story of a guy pulling out from a parking space behind a DeHavilland Dash 7 taxiing by in the opposite direction.  He found himself behind the Dash 7 facing away from it, with full up elevator, just as the Dash 7 made a big shot of power on one side to make a sharp turn.  The up elevator into the prop blast from behind actually flipped him over.  As the tail came up, he had no idea what was happening and just pulled harder.

It just reduces the load/wear-and-tear on the nose gear a bit, and keeps prop a little farther away from the ground.  Even smooth looking paved taxiways and ramp areas usually have all kinds of small stones and gravel fragments, and propellers love to suck them up and create all those little dings on the prop leading edge.
This is especially important during run up, and at the start of the takeoff roll where thrust wants to pull the nose down and the propeller tips get to only a few inches from the surface, but it's also a good habit to do all the time in a plane like a 172. It's also a good practice, if you own your own plane and have to pay for the repairs, to do your runups on grass if that is at all possible. That is a huge propeller saver.
If there is a strong tailwind component however, holding the elevator up does nothing, or actually increases the nose wheel load if there is a net tailwind that overcomes the prop blast, so in those cases, you generally taxi with the elevator neutral. You will notice the effect if you are paying attention and the winds are strong enough.

I would get another opinion, my 141 school did not teach this. They only taught to hold full aft whenever taxiing/takeoff on soft fields, and short field takeoff.
Just because the instructor told you doesn't mean it's right... I was taught a wrong procedure before, and have heard of egregious stuff not taught like not leaning at altitude, etc.
From AFH 2-19 to 2-20:

When taxiing at appropriate speeds in no-wind conditions, the aileron
and elevator control surfaces have little or no effect on  directional
control of the airplane. These controls should not be considered
steering devices and should be held in a neutral position.
When taxiing with a quartering headwind, the wing on the upwind side
(the side that the wind is coming from) tends to be lifted by  the
wind unless the aileron control is held in that direction (upwind
aileron UP). Moving the aileron into the UP position reduces the
effect of the wind striking that wing, thus reducing the lifting
action. This control movement also causes the downwind aileron to be
placed in the DOWN position, thus a small amount of lift and drag on
the downwind wing, further reducing the tendency of  the upwind wing
to rise. [Figure 2-15]
When taxiing with a quartering tailwind, the elevator should be held
in the DOWN position, and the upwind aileron, DOWN. Since  the wind is
striking the airplane from behind, these control positions reduce the
tendency of the wind to get under the tail and the  wing and to nose
the airplane over. The application of these crosswind taxi corrections
helps to minimize the weathervaning tendency  and ultimately results
in easier steering. [Figure 2-15]
The presence of moderate to strong headwinds and/or a strong propeller
slipstream creates lift on the horizontal tail surfaces  and makes it
necessary to control the pitch attitude while taxiing. The elevator
control in nosewheel-type airplanes should be held  in the neutral
position, while in tailwheel-type airplanes, it should be held in the
full aft position to hold the tail down unless  the headwind gets very
strong, which allows for an elevator position closer to neutral.

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Responding to another aircraft without knowing their radio call sign
PPL student here. I recently had someone ask over the radio if there was any traffic in the pattern (uncontrolled class G airport). I could make out everything that pilot said except for his radio call sign. (I'm still struggling a bit with understanding certain transmissions due to the "radio effect" and other interferences).
What is the appropriate thing to do when you want to respond to a transmission but couldn't make out the sender's radio call sign?
In this particular case I responded anyway, without addressing them explicitly, which didn't feel 100% "by the book". I later thought leading my response with "Calling aircraft..." might have been appropriate, but I'm not sure.

Non-towered airports are a bit less "by the book" than towered airports in general.  More important than strict protocol and the stress that can bring upon new pilots, the most important thing to remember about communications is that the purpose is to...
...communicate.
Didn't catch his side number?  He/she doesn't care, they just want to know where you are in the pattern.  Simply key the mic and say something like "aircraft calling Binford traffic, N1234, it's just me in the pattern, red and white Cessna 152, midfield, left downwind runway 36."
Disclaimer:  Italicized text in my example above is non-standard and some won't like it, but it's folksy and real, and not a big deal between two people at a small country airport enjoying the freedom of the skies on a sunny day...

Agree that exact phraseology is far less important in this sort of situation than communicating. If the "aircraft calling" gets what he needs from your one transmission then that's a success. Might add an abbreviated callsign at the end, just so the next time you call turning base (or whatever call you make next), there's no question if that is the same aircraft that answered as "just me" earlier. But that's a nitpick. When plain English best conveys the necessary information, that's what's worth using!

@RalphJ, good point, I added callsign to the example.  Thanks!

In fact since common practice is to simply make position callouts addressed to “ traffic” anyway. I’d probably just take that as an opportunity to make a normal position callout.

Good answer. Small improvement is to not say "its just me in the pattern" as you cannot be sure. Say something like "not aware of any other trafiic", or "believe I am only one i pattern".

"Station calling" is standard in both amateur radio and, I believe, Marine VHF, so it's not at all surprising that "aircraft calling" is the aviation equivalent...

@ghellquist, I get your point and agree to an extent, but if you are doing touch and goes and don't know whether or not there are any other planes in the pattern with you, there are bigger problems to deal with than how to respond to inbound traffic on the radio.  Situational awareness... it isn't optional!!!  Again, my point was to intentionally included a snippet of real world non-standard phraseology to break through the rigid mindset that can lock up new pilots and lead to stilted, robotic transmissions in an attempt to be professional and 100% "correct", not to provide a perfect example.

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Measuring speed and altitude from personal phone midflight
Given that there is no need now for one to swith off their cellphone midflight, inflight wifi is now  a norm and common, Is it possible for me to measure the velocity and altitude of an aircraft using my personal car GPS speed indicator or cellphone app in the case of speed and altitude as a passenger?

Would GPS signals be detected inside the body of an airliner?  Non-composite ones would seem to make a pretty good Faraday cage.

Yes. Airplane mode generally only includes transmitters, and GPS is receive-only. The below is a screenshot I made with a speedometer app, on an Airbus A320. I had to hold the phone near the window to get GPS coverage. (Units: km/h groundspeed)

On a more recent flight, I could even get GPS coverage away from the window, in a Boeing 737-200 (although I was seated next to the overwing exit).
Note that some altimeter apps may use the phone's barometer, which will only give you the cabin altitude.

I was confused for a minute until I realised your average speedometer app obviously does not use knots ...

@J.Hougaard I was just about to submit an edit when I got a call. It's indeed km/h, from an app called DigiHUD which I used in a car with a dodgy speedometer (it can do a mirror image to get that F-16 HUD feel on your windscreen until you corner too tightly and have your phone fly of off the dashboard)

Depending on the reliability of the sensors in your phone, yes that sounds completely possible. Most modern aircraft use GNSS for navigation, and your phone relies on the exact same technology.
Be aware that you will get the ground speed - see this question for further details: Why is there a difference between GPS Speed and Indicator speed?

Theoretically there are legal limits to use a GPS receiver on moving vehicles (did I say missiles?): 1,000 kt and 18,000 m, and US GPS receivers should enforce these limits. This is compatible with today airliners, but in some cases this creates problems.

Similar to speed, the altitude that the gps reads is not pressure altitude.

@mins I had never heard of that before. That's completely silly. If someone is capable of engineering a high speed, high altitude GPS guided missile I'm sure they're not using a cell phone for guidance

@TomMcW: But they might well buy an off-the-shelf GPS reciever module that is manufactured by the millions (hence cheap) for use in cell phones.  E.g. https://www.digikey.com/products/en/uncategorized/miscellaneous/49?k=gps or https://www.sparkfun.com/search/results?term=gps

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Can a turbojet jet or turbofan powered aircraft land and take off from water?
Can a turbojet jet or turbofan powered aircraft land and take off from water?  How much clearence from the water surface would it need for its engines so that it does not suck up water?

There are several Beriev amphibians powered by turbofans, supposedly in production.

https://en.wikipedia.org/wiki/Beriev_Be-200  Includes pictures of it in use.

Yes, they can.
In service today:
The Canadair CL415 is a turboprop water bomber with water landing capabilities (typically, water skimming capabilities, to skim across a lake and refill).
The Shin Maywa US-2 is the latest in a series of rescue/maritime patrol aircraft that have been in service for some time. The design uses the engines and wing of a C-130, with an interesting STOL feature: ducts that blow air across the top of the flaps so that they can be set at a more extreme angle for extremely short takeoff.
The Beriev BE-200 has seen limited production in Russia. It uses high bypass turbofans, mounted high and behind the wings to protect the engines from water spray.
From the Soviet era, were the ekranoplan sea skimmers, that flew entirely in ground effects. All were turbine powered.
In a prototype stage is the AVIC AG-600 in China. Powered by four turboprops, it appears to be an upsized copy of the Shin Maywa design.
A one-off production flying today is the Doriner DO-24ATT, essentially a WW2 DO-24 maritime patrol aircraft that was re-engined with turboprops. It is currently flown by Claudius Doriner's grandson.
Four turbine powered amphibious/flying boat aircraft that were developed but never saw service were the Convair Sea Dart, Martin SeaMaster, Saunders-Roe Princess, and Saunders-Roe SRA1.

The Do-24 ATT also has a new and much improved wing.

The question asked for turbofan or turbojet aircraft. All on your list except the BE-200 are turboprops.

Note that the concern is not about water spray. That problem is no worse for turbines than pistons, likely less. The concern is about vortex like this sucking the water from the surface, which is only concern for turbojets and turbofans due to their much higher mass flow through the engine.

Yes, if it's designed to do so.  There have been several jet seaplanes over the years, and one feature common to almost all of them is that the engine intake(s) are mounted above the wings or high on (or above!) the fuselage (sometimes on an auxiliary pair of high-mounted stub wings) to avoid ingesting water.
Martin P6M (intakes - and engines - on top of the wings):

(Source)
Convair F2Y (intakes on upper fuselage; notable as the only seaplane ever to break Mach 1):

(Source)
Beriev Be-200 (engines and intakes mounted on top of fuselage):

(Source)
There are a couple of interesting exceptions to the "intakes up top" rule:

The Beriev Be-10 had intakes on the sides of the bow, relying on spray fences to protect them from water ingestion; apparently, raised intakes were tested at one point, but found to seriously degrade the aircraft's performance.
The Saunders-Roe SR.A/1 had the intake for its engines at the tip of its bow, presumably in order to get air not yet contaminated by spray.

And, of course, in an emergency, even jets not designed for water operations can land on water if need be, although the plane probably won't be flyable afterwards.


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Are modern fighter jets bulletproof and armored?
Are modern fighter jets bulletproof and armored? One would not be wrong given part of their operations is being on the receiving end of enemy ammunition shooting at them.

With very select exceptions like the Su-34, and the A-10 if you consider it modern, they are not. Even in these cases only the pilot and a few critical parts are armored. Most of the aircraft's skin offers no meaningful resistance even to small arms.
Extensive armor coverage that could withstand modern air-to-air or surface-to-air weapons simply isn't viable for a fighter for weight reasons. Redundancy is used to resist near misses and light hits instead.
The reasons are different depending on the weapon. MANPADS like the Stinger go for the nearest heat source (engine exhaust). Their capabilities against a fighter are limited to fringe cases (flying too low, caught on landing/takeoff, and a very lucky shot), and armoring the engine nozzle isn't viable anyway.
The lightest effective anti-aircraft weapon, the Sidewinder, uses a continuous rod warhead, a ring of steel expanding at almost 1 km/s. Due to high inertia, it will cut through anything except for the engine, major bulkheads and longerons, and hard elements like the A-10's "titanium bathtub". Aramid lining, which is the only thing a modern fighter could afford weight-wise for full-airframe protection, will be cut.
The heaviest is the S-400 SAM, which intercepts the target at 2 km/s with a 180 kg fragmentation warhead. The resulting hypervelocity impact (3+ km/s) has solids behave like liquids, with impact results determined by mass rather than strength. The low odds of surviving a warhead this size aside, when it's mass that determines these odds, it's always better invested in something functional rather than just armor.
Most mid-size AAM and SAM also fly an intercept course at high velocity and use high-brisance explosives for blast fragmentation. Against resulting high impact velocities, mass is better invested in more redundant hardware, not armor. That is very different from low velocities, common on the ground, where thin layers of high-strength materials can prevent projectile penetration.
Larger fighters are indeed more resistant to damage than smaller lighter ones (see the one-wing F-15). Armoring a few critical elements can help improve survivability, but this armor has to be very localized. The Su-27 family has an armor plate between the engines, so that one wouldn't damage the other if it disintegrates after a hit. Close air support (CAS) aircraft that attack tanks and other ground vehicles carry some protection for the pilot - notoriously vulnerable to punctures, unlike most of the plane - against ground fire.
A combination of these factors is why armor has largely become limited to CAS aircraft: high-strength armor is very weight-effective against the low velocities of land warfare weapons, but much less so against hypervelocity impactors and fragments used in air combat.
See a related question for a few more bits of info on aircraft armor and protection:
Why do modern fighter jets use 20mm guns?

Might be worth noting what CAS stands for

Some are. Most notably the A-10 Warthog carries about 1200 LBS of titanium armor up front to protect the cockpit.
A lot of modern fighters have self sealing fuel tanks which is a type of bulletproofing in a sense. It allows the airframes fuel tanks to be hit, but unaffected by bullet fire.
Broadly speaking additional armor adds weight which is generally viewed as a bad thing in aviation.
Aircraft designs also focus on things like redundancy so that they can be hit by multiple rounds of ammunition and have backup systems in place if and when a bullet strike takes out an important system.
There is some more discussion here.

Note that the A-10 Warthog is armored this way precisely because it is not a fighter, it is a ground attack aircraft. It is specifically designed to be shot at, i.e. to fly low and slow above and across an active battlefield. It's closer to a tank than to a fighter in that respect. It is an airframe quite literally built around a huge gun, with a high focus on survivability: the high mounted engines, twin control surfaces, multiply redundant control systems, and the titanium tub the pilot and critical control systems sit in.

My favorite sentence from the Wikipedia article: "The aircraft is designed to be able to fly with one engine, one half of the tail, one elevator, and half of a wing missing".

Generally speaking, armor is contradictory to flying. Besides, modern fighters fly so high above any small arms fire, at the very least at 10,000 ft, that bullets simply isn't even a very remote concern to fighters. Fighters are much tougher than they were back in WWII, but that's because they must sustain the high G load at high-speed cornering rather than the need to survive gunfire.
However, if we are talking about cannon fire, then it is a very real concern to modern fighters. The US uses 20mm, the Europeans 27mm and the Russians prefer 30mm. Each shot from any of these rapid firing cannons can outright blow a hole in any aircraft, and there is no way any amount of armor against these big guns can be added to fighters without making them too heavy to fly. Fortunately, the unpowered projectiles from these guns can only fly for less than 2 miles before their trajectories start to droop significantly, so generally, fighters rarely get a chance to use these armaments in real combats.
The real threat to modern fighters is air-to-air missiles that they themselves are armed with and surface-to-air missiles. As long as fighters keep away from these threats absolutely nothing can shoot them down. As long as these two kinds of missiles are not a real concern after the enemy air force and SAM batteries are dealt with, fighters can fly with near impunity.
The A-10 is a CAS aircraft, and it is used against cheap targets that aren't worth smart bombs or air-to-surface missiles. CAS is not in vogue anymore, and the USAF keep them because they cost so little, not because they have to fly almost face to face against the enemies. Besides, the armor A-10 is carrying isn't real armor. Real armor stops or bounces back projectiles, the A-10's armor absorbs the projectile without letting it through.

I'm surprised as to why you'd consider the A-10's armor to be "not real". First of all, being titanium, it will stop/bounce back projectiles just as well. Second, main battle tank armor is definitely real, and most of it is designed to "absorb" the projectile. Both KEP (APFSDS) and HEAT, which are the only viable threats to modern tanks in the frontal arc, cannot be stopped or bounced except at very oblique (85+ degree) angles due to their hypervelocity nature introducing liquid-like behavior in materials, but are rather "absorbed" by the armor.

@Therac Don't most modern battle tanks use reactive armor?

@TomMcW Reactive armor is a layer placed on top of normal composite armor, used to break up HEAT jets and sometimes KEP. It's only an addition (or rather an effectiveness multiplier) for passive armor.


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Do cellphones have the technology to measure altitude through an App
Do cellphones have the technology to measure altitude through an App as they do speed and GPS.

If are measuring your position by GPS then by definition you also get speed and altitude.

This seems very similar to your previous question, and see also this one

Yes.
GPS gives altitude, not just location on the surface, so any cell phone with GPS capability can determine the altitude that way.
Some cell phones also have air pressure sensors that apps can use to calculate the pressure altitude. In my experience, these sensors are sensitive to a single foot of altitude change, but I don't know how accurate they are overall.

Note that the air pressure sensor will display the cabin pressurization altitude, not true altitude, though that is also interesting information for passengers. As to how accurate GPS positioning is: it's getting better, as accuracy is largely a function of the computational power of the phone.

GPS "altitude" is not really "altitude", it is the height above the reference geoid which is typically WGS84.

Any app that has access to GPS can do this. Mobile GPS reports your position in three dimensions, along with an inferred accuracy, in metres.
This is sometimes called "fine position" or "high accuracy position" (to distinguish it from "coarse position", which is based on cell tower's location, which you obviously don't have at altitude).
As Ron Beyer importantly pointed out, this is in relation to a reference geoid (see WGS 84).
Years ago I wrote a toy web application proof-of-concept to do just that. For fun, I'm currently working on an updated version. (It's a toy for passengers, and obviously not appropriate for navigation.)
Something like ForeFlight is far, far fancier.

I'm going to go against the other two answers here and say "no"...
GPS provides an "altitude", but that distance is the distance above the reference geoid (WGS84), not true altitude above the ground. For simplicity sake let's say that there are two altitudes used in aviation, pressure altitude and the distance above the ground (AGL)...
A phone may be able to measure pressure altitude. Some phones have pressure sensors in them but they may not accurately show the altitude because either you are flying in a pressurized aircraft, or if you are flying something unpressurized the cabin pressure may still differ from the outside pressure by a little bit (many aircraft manuals reference altimeter errors when using the alternate static source, which is located inside the aircraft).
What a phone really can't do is measure AGL, which is the distance above the ground (hard surface). This requires radio altimeters or some other method of correlating your current position, pressure altitude, and the ground level.
So if you are looking for your phone to match what is being displayed in the cockpit on the altimeter, it probably won't match. It may give a reasonable value that can be used in an emergency, but I wouldn't count on it.
Apps like Foreflight or Garmin Pilot use GPS location and map data to calculate an approximate altitude. If you connect them to the cockpit equipment (like an ADS-B with altitude reporting), it will use the same altitude that is being sent out for your ADS-B, which again, may or may not be the same thing that is displayed on your altimeter.

GPS gives HAE, height above ellipsoid, unless there's a geoid model available to convert to a geoid (roughly mean sea level) height.


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Is it economically profitable for airports use jetties that use all the airbus A380's 16 exits at the same time
Does it make economic sense or is it economically profitable for airports to build jetties or jetty facilities that use all the airbus A380's 16 exits at the same time.  This would be very convinient for passengers with less time waiting in a que to embark and disembark the aircraft and would be beneficial to airliners because they'd spend less time waiting for passengers to disembark the aircraft, cleaning crews entering the plane quicker getting it ready for a new set of passengers sooner who would enter the plane quicker.  They'd also pay less for parking space at airports as they'd spend less time there.  The airports would free up their parking spaces quicker and would service more planes per day and get more revenue. Win... Win... Win!!!

See also How long does it take to refuel a big jumbo jet?.  Since passenger loading isn't critical path, making it quicker won't change the time the plane spends at the gate.

Since Airbus has discontinued the A380, it would make very little economical sense at this point to begin the redesign process for an aircraft whose numbers will only decrease over time.


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Is a non-WAAS Garmin 530 certified for an LNAV/VNAV approach?
I may not understand all the details of what I'm asking but trying to wrap my head around it.
I am aware that before WAAS, some GPS aircraft were equipped to get vertical guidance by a Barocorrected altitude information sent to the FMS and along with the non-waas GPS could calculate (interpolate) glide path info and were approved to fly LNAV/VNAV approaches.
My question is whether the non-waas Garmin 530 has the ability and necessary FAA approval to perform this and if it is an option?

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Is it possible to counter and minimise g forces for more speed by design or technology
Apparently humans can survive betwee 3 G and 5 G G-forces.  Is it possible by design or technology to invent and incorporate that technology or design in passenger planes should we surpass all impedements to speed as a species and left with G forces as the only problem.  Fast trans and cars lately tilt the railway or road, or the body of a car or train tils at curves allowing greater turning speed and no overturing.

I'm not sure what you mean by "incorporate that technology or design". Which technology or design are you talking about? Are you asking if it's possible to reduce the g-forces that passengers feel, so that, for example, maybe an aircraft could accelerate at 6 g while the passengers only feel 4 g?

How would people in a passenger jet be subjected to 3G in the first place?

The important thing to consider about humans surviving more (or less) than 1g is: for how much time?

In straight and level flight, 1g is all you’ll ever get regardless of speed. If you can afford wide turns and only moderate accelerations, g protection isn’t required at all (for any speed).

The tilting you described is a way to lessen the effects of G forces on the body.  There are other ways to lessen the effects such as G-suits like military pilots wear, and tilting the seats back to redirect the force.  (as is done in the F-16)
However, it is not possible to reduce or eliminate actual G forces.  This is basic Newtonian physics, and is pretty much absolute.


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Are hydraulic retractible landing gear possible
One of the impediments and drawbacks to extending landing gear in light of building larger engines are the larger space required for the taller gear.  Would hydraulic retractable gear that works as a truck jack (for changing tyres) that utilizes the same space but however taller gear work with aircraft and is it feasible and would it add extra weight.  Would this system be able to use current hydraulic systems without significant additions?

Source

As far as I'm aware, all current commercial airliners (with retractable gear) use hydraulics to extend/retract the gear. Are you referring to a system that uses a straight cylinder as pictured instead of the current folding gear?

Even small planes use hydraulic landing gear. There are few, if any, strictly mechanical gear retraction systems.

@FreeMan yes I mean a straight cylinder that retracts and extends and then folds, so that it may still fit in the original bay

I think you mean gear legs that can hydraulically grow longer when they extend and shorter when they retract so you can have a longer gear that fits in the same gear bay.
It's been done on military designs.  The Avro Arrow's Dowty designed main gear legs hydraulically lengthened and shortened, something like 8 inches or so, during extension and retraction, using a telescoping strut section separate from the shock absorbing section at the bottom, due to a limited envelope in the wing (they also had to make the wheel truck rotate to go flat in the wing because the leg retracts at a forward angle - a complicated mess).

Anyway, a complex and heavy solution, which is why you don't see it much.  Not sure if it's ever been tried on a civilian airliner, but I'm sure it's at least been attempted some time some where.

The NLG of the 737 MAX-10 also extends by 9" (IIRC). There was something posted about this on another question.

@ymb1 that makes more sense - I was trying to figure out how an NLG extension would prevent tail strikes...


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What is the minimum and maximum number of jet bridges used on an Airbus A380?
What is the minimum and maximum number of jet bridges used for embarking and disembarking on a typical Airbus A380 trip and why?


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How long does it take to assemble an Airbus A380?
How long does it take to assemble an Airbus A380?

Probably best to only consider assembly, if a compressor blade was made then sat in storage for a year you wouldn’t want to count that time in the estimate (and yes that does happen).

The timeline to build out each component of an Airbus A380 and the final assembly of the components are two different things. I will focus on final assembly.
Once all the parts are available, the time it takes for the final assembly the fuselage, the wings and other components in the jig at Station 40 is about a week. Add to that an additional month for testing the assembled components, customization and painting before delivering the plane to a customer.
When the assembly line is working at full speed, Airbus can deliver about 30 A380 planes a year, doing so in 2012 and 2014. In 2018, the assembly line is working at a significantly reduced output of 12 planes per year (1 per month) to keep the plane in production for as long as possible in hopes that additional orders will be placed to extend the life of the platform.

https://en.wikipedia.org/wiki/Airbus_A380
https://www.cnet.com/news/building-the-a380-the-worlds-largest-passenger-plane/

Good luck figuring out the timeline of how long it takes to assemble the individual components like the cockpit, the engines, the wings, 330 miles of wiring, you get the idea. The reason it's hard to determine things like the timeline for the wiring is that much of the wiring is done before the components are installed together into one physical unit.

@securitydude5.  This reference also states the current A380 production rate is 1 per month. https://airwaysmag.com/industry/a-look-at-the-remaining-airbus-a380-and-boeing-747-orders-deliveries/

Airplanes are not built like cars where after completion, they are showcased at dealership to attract prospective buyers. For larger commercial airplanes, airlines place an order first and then wait for the airplanes to be manufactured, custom modifications completed, inspected by the airline and then delivered. It is a bit complicated process.
However, one of the A380s Emirates ordered, was manufactured and delivered in 80 days:

Emirates are celebrating having their fiftieth Airbus A380 in service
  with the release of footage showing how 800 workers across Europe came
  together to build the biggest passenger jet in the sky in just 80
  days.

Demand for the large airplanes can vary significantly month-to-month and year-to-year, and the manufacturers adjust their production rate to match demand.
Typical rates for the biggest airplanes are about 1 a month, while planes like the extremely popular Boeing 737 can be produced around 42-47 a month! (Source: Boeing)
Manufacturing large airplanes takes hundreds of people on the assembly line.
The variations in production rate are managed by changing the staffing levels on the assembly line. When planes are in high demand, more people and more shifts are added to make planes faster. When demand is low, shifts and individuals may be laid off to slow production.
Of course, no one wants to be constantly hiring and firing skilled assembly line workers, so carefully managing the backlog of orders, the expected rate of future orders, and the number of people working is crucial to keeping employment relatively stable. Management wants to produce planes as fast as their customers need them, but not so fast that they have to layoff large numbers of people when a single airplane order is missed.
With a fully staffed line working fast, large planes can be produced, start-to-finish, in less than 2 months. Typically, however, the biggest planes take around 6 months to make.

You did not talk about A380 at all. And all you presented is without any reference. I would like to know how you found that 30+ B737s are manufactured every month.

Source:  I used to live within walking distance of the 737 factory in Renton, WA.   I walked my dogs on the Cedar River Trail, and watched between 6 and 12 planes get finished every week.  On weekends, they all depart in rapid succession to go get painted and finished.

Boeing's own page says 42 to 47 a month: http://www.boeing.com/company/about-bca/washington/737-rate-increase-07-28-17.page

The point of my answer is that there is no canonical, correct answer for "how long does it take to make an A380".  The answer is, "it depends", and I described many of the key variables that factor into it.

No hard feelings, but downvoted because with the exception of the last paragraph, the rest of the answer does not answer the question. Production rate has nothing to do with how long it takes to build a plane. Analogy: a restaurant can finish 30 dishes per hour. It has nothing to do with how long it takes to make one dish.

@kevin It's not entirely accurate to say that production rate and time are unrelated. If you want to increase rate, you either have to add more lines or build them faster. Both are valid and have their pros and cons.


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How is the area of flaps determined?
While may be possible to look up the dimensions of high lift devices in an aicraft's documentation, there is no information on what the underlying design choices are.
Using Wikipedia, I found out that flaps are used to increase the wing camber, to increase the wing's lift coefficient and decrease stall speed. However, there is no information on how much extra camber is desirable, and how the surface area of the flaps relate to the camber increase.
So, how exactly are the dimensions for flaps on an aircraft chosen? While I'm specifically wondering about large airliners, such as an Airbus A380, I would also like to know if the method for determining the flap size is generally the same for all aircraft, or if there are differences depending on size or mission profile.


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Are high bypass turbo jet engines suitable for tail and body mounted engines
Are high bypass turbo jet engines suitable for tail and body mounted engines.  If not what are the drawbacks, danger if so, are there any anycraft with any such setup?

it depends on what you call 'high-bypass'. The RB.211 engine was tested in a tail mount on a VC-10:

For tail-mounted high-bypass engines, the engine mount gets long, which means it gets heavy.
Tail- and bodymounted engines in general have drawbacks that also apply to high-bypass engines:

the high position means maintenance access requires special equipment and takes longer
for bodymounted engines, engine choices are limited by the amount of space available (unless you redesign this part of the fuselage, which can get expensive)


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What keeps certified GA aircraft from being affordable?
A personal (pipe) dream of mine is to own a new aircraft, but the costs for certified GA aircraft is borderline outrageous. A new Cessna 172, considered an entry level aircraft, can go for well over \$250,000 new. The Icon A5, an entry level light sport goes for about \$190,000 for the base model.
Not discounting the engineering process or tooling required, but what really keeps the price of these aircraft so high? Is it possible that a company could bring an aircraft to market that is comparable to the A5 below the \$100,000 mark? I find it hard to imagine that a company couldn't take an aircraft like the SeaRey, certify it, and get it out for a reasonable price.
So the question is, what are the factors that make certified GA aircraft so expensive, especially for established companies like Cessna, Piper, or others? Does the mere presence of an FAA certification command a premium price?

I don't know about you, but I'd be happy to pay the extra 90k for an Icon A5 instead of asking for a bargain basement flying coffin. If your 5k Geely car conks out, it rolls to a stop. If your $20,000 bargain bin prop engine on a 100k plane conks out, and you don't have enough airspeed/altitude to land safely, you will crash and quite possibly die. Gravity is a harsh mistress. I wouldn't skimp on cost when building a machine that intends to fight her and win.

I'm not saying sacrifice quality,  I'm wondering where the cost is,  I wouldn't consider the SeaRey a "flying coffin", even in its homebuilt form. I wouldn't suggest any certifications be cut...

What I'm asking is if the certifications add that much cost to each component that it can't be amortized to zero over 10k units for example. It doesn't have to be glass cockpit, a 6 pack works just fine and isn't any less safe (arguably more so).

There are plenty of perfectly safe LSAs for below 100,000.  The Aerotrek and MVP.aero come to mind.  There's a whole slew of information about LSAs at www.bydanjohnson.com if you're curious.  It's mostly certified LSAs on there, which have their limitations but are perfectly viable for learning to fly and short trips.

MVP Aero is retailing for $219,000, I'll look at the other things you mentioned but would still like to understand what makes am entry level aircraft so expensive...

You can buy used Lancair. Maybe 360. Super aircraft. May dream :) Even some Cessna models were developed from them.

BTW Why do you need certification? Usually people try to get rid of it whatever possible?

@Andrius I'm using "ready-to-fly" off the factory floor aircraft, which usually means certified, as a reference. As much as I'm sure I'd enjoy spending years building an aircraft I'm more of an instant gratification person.

I think you'll find that the cost of maintaining an aircraft over a period of time kind of outweighs the fly-away cost of the plane.

I understand that you need "ready-to-fly" but it's possible to by an aircraft that was build by someone else. Of course there is some risk but there is a big market and possible to find good airplanes.

Also keep in mind that if you buy certified aircraft it makes sense that it flies a lot! Because you will have to do maintenance based on time even if you have flown 0 hours. And of course it will be expensive.

You can also consider buying the new plane with a friend or two, share the pain that way. Need to schedule out who flies it when and set aside some money by the hour flown towards maintenance, or divide the maintenance bill by the hours flown.  Nice thing about single ownership is you can go when you want to go, change what you want to change, all on your own schedule.

Tradeaplane has 19 Cessna 177s for same, one is a nice looking 1978RG with Garmin NAV/COM/GPS and ADSB In/out. Pick that up, put in some newer avionics (couple of Garmin G5s, ditch the vacuum system, maybe update the autpilot), have a really nice flying airplane for quite a few years before engine overhaul might need to be considered.  https://www.trade-a-plane.com/search?category_level1=Single+Engine+Piston&make=CESSNA&model_group=CESSNA+177+SERIES&s-type=aircraft

FYI, the Icon A5 fully-equipped is $359,000 MSRP (U.S. delivery).

Low volume, high liability, and the overhead of certification all contribute to the high price of factory-new aircraft.
Certification
The process to design, build, and test an aircraft to receive a type certificate from the FAA adds time and cost to any new clean-sheet design (substantially more cost if the design is novel in some way).
The design and construction techniques must conform to the requirements in the FARs, and you have to demonstrate conformance to FAA inspectors (who will also want to see you assemble a few planes under their oversight before issuing you a production certificate to go ahead and make them on your own).
Volume
50+ year old designs like the Piper PA-28 and Cessna 172 that are still in production on an approved type certificate avoid that cost, but are still a low-volume high-touch product: Here's a wing being assembled.
Because of the relatively low demand (and thus low sales volume) the cost of the skilled personnel to build aircraft isn't spread out the way it is with cars (and the investment in large-scale low-touch automation isn't economically feasible). That drives up the manufacturing cost, and the price goes up with it to ensure the manufacturer is still making a profit.
Similar economies of scale affect all the third-party parts going into new planes as well: radios, instruments, lights, etc. that conform to applicable FAA Technical Standard Orders (TSOs) are rather expensive.
Liability
Finally, any new aircraft starts a new 18-year liability period for the manufacturer. Any accident that results in whole or in part from manufacturer errors, omissions, or negligence in a new aircraft can come back to haunt that manufacturer in the form of a lawsuit, so the cost of product liability insurance is baked into the price of every new aircraft. (After 18 years the manufacturer is off the hook thanks to the General Aviation Revitalization Act.)
All of these factors take the Searey from being a \$50,000 kit (airframe, engine, and propeller) to a \$150,000 factory-built Light Sport aircraft, and that is putting it on the market as a Light Sport aircraft under "consensus industry standards". Producing it as a Part 23 certificated aircraft would add the additional cost and requirements of FAA certification.
(I'm using the Searey as a convenient example since you mentioned it in your question and I could find kit and factory-built pricing easily, but other light sport aircraft available in both kit and factory models seem to stack up similarly. I don't know of any that have been subsequently "upgraded" to a Part 23 aircraft: Only a few manufacturers have successfully launched that sort of product, and those command rather substantial prices on the new market.)

Yeah the volume & number of manufacturers is the issue: too much competition to risk the high investment cost to bring the unit cost down, not enough of a market to guarantee a ROI on that investment in face of heavy competition. Quite simply, you could produce a plane that cheaply, but the investment would be a huge risk nobody is willing to take. A typical modern high-volume car factory is perhaps $5bn to build with tooling and robotics. That's 50,000x $100k aircraft you need to sell to break even, ignoring the material costs of the aircraft which probably doubles that to 100,000+ needed

...for comparison, Cessna has built 40-45k 172's in the last 60 years. The numbers just don't add up

I agree with the answer, but I still find it odd that an aviation 4 cylinder 180 HP engine designed in the 50s still costs more than a nice car with equivalent HP.

@GregTaylor: Same thing, really. You need to make sure the engine still works if it's banked 30 degrees to the right, and pitched 10 degrees down. Technically that's not very complex, but doing that in an FAA-certified way isn't cheap, and then you still have small production volumes.

I can agree that the 172's wing is labor intensive, however with new composite materials and manufacturing processes I can't see that a wing couldn't be mass produced (even at the 5k quantity) for less cost. I also didn't think about liability insurance, but does it add that much to each airframe?

@JonStory I'm not sure I can agree with the numbers. A high volume car factory and a much lower volume aircraft factory are very different in costs. It doesn't take an equivalent of a huge car factory churning out hundreds of cars a day to make an aircraft at the rate of 1/day. Otherwise it wouldn't be a sustainable prospect for any company, Cessna, Piper, Icon, etc. Plus resources can be pooled, much in the way that Cirrus builds components for Icon.

No but the cost of automatic 'hands off' tooling is very high regardless of the number you're producing. You say it wouldn't be sustainable for those companies.... It isn't, that's why they don't do it and why aircraft are so expensive

It's worth noting that some sectors of the aviation industry ARE investing in the automated tooling: Both major engine makers (Continental & Lycoming) have made substantial investments in CNC equipment to help streamline their manufacturing processes.

Product liability destroyed this industry.
In the 1970s GA aircraft were much less expensive. A midrange model cost about twice the annual salary of the average US worker. Annual production was about 14k per year.
Then attorneys found out that juries could be persuaded to award ten times as much for a death in a small airplane as for the equivalent death in a car. Deep pockets law put manufacturers on the hook for compensation even though most accidents were due to pilot error, just as in cars. Product liability cost soared, rising from single digit thousands of dollars per aircraft sold to a hundred thousand. Purchase prices rose dramatically, driving demand lower. This increased unit production cost since fixed costs were now spread across fewer units.
By mid 1980 production had fallen to 800 units per year, and the cost of a midrange model had climbed to ten times the average US worker salary. All three primary manufacturers went bankrupt and the industry has never recovered.
Lack of funds has made the byzantine and costly certification process a nearly impossible obstacle, allowing very little new technology or new aircraft to be introduced, except in very expensive models. Certification cost has created effective monopolies in both airframes and parts. Aircraft engines cost ten times as much as similar power automobile engines. Most aircraft now flying are more than 35 years old, having been made prior to the collapse. Cars get refreshed about every five years or sales disintegrate.
The Harvard study, The Uneasy Case for Product Liability, describes how the intended purpose of product liability, improvement in product safety, is often frustrated by the excessive cost of the legal system. It discusses aircraft along with other consumer goods, and is an interesting read on the subject.

Piper and Mooney have entered bankruptcy proceedings several times each but Cessna and Beechcraft weathered the 1980s without bankruptcy. Cessna stopped light GA aircraft production completely focusing instead on jets and the freight hauling C208. Beechcraft never completely ceased production of its GA aircraft though production numbers were low. They went through several sales/mergers and did file for bankruptcy as part of Hawker-Beechcraft in 2012 and were just about to declare bankruptcy in 2013 when they were acquired by Textron—who also own Cessna.

@JScarry Technically correct, though Cessna was forced to sell itself to General Dynamics in the '80s on the brink of bankruptcy, after burning through the cash it raised from selling its avionics business to Sperry. GD only cared about Cessna's jets and maybe turboprops; the piston business was dead and killing the rest of the company.

Why can't product liability laws require that the plaintiff prove beyond reasonable doubt, or at least with clear and convincing evidence, that the manufacturer is liable, rather than a preponderance of the evidence? It would be unusual for non-criminal laws, but I doubt it would be unconstitutional.


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How to keep a Garmin GTX330 turned off when powering on avionics?
There seems to be an option in the GTX 330 settings that keeps to unit from powering on when receiveing power from the power system.
I flew in two different airplanes and one immediately powered on the transponder, the other one keeps the transponder turned off, until I press ON.
Looking thru the Pilot's Guide and Installation Manual didn't give me any clue.
Can someone help? Seems like an undocumented feature.

In the manual I see the device does have the OFF button on the panel. Have you tried to switch it off with that button before removing the external power? After powering up, it would be logical for the device to return into the state where it was when the power was removed.

It turns on automatically when a certain altitude has been reached. I try to keep it also from that behaviour.

@David It doesn’t turn on automatically when takeoff is sensed, it changes from GND to ALT. The FAA recommends that you always be in ALT mode—even when on the ground—since many airports can now track you on the ground. There are settings that let you configure it to always be in ALT mode. You are required to be transmitting whenever you are in the air, so why would you want to turn it off?

I don't know, but I suspect it's a question of how the unit was installed. The manual says (emphasis mine) "The GTX 330 transponder is powered on by pressing the STBY, ALT or ON keys, or by a remote avionics master switch (if applicable)." It seems possible that one aircraft has it connected to the avionics master and one doesn't.

You might get a more useful answer if you can explain why you want to do this. And if the unit is on its own circuit breaker, you can always just pull that out.

If pin number 1 on the back of the GTX330 unit is connected to power (+), the unit will turn on. If it is not, you will have to manually press the on button. If you remove power from pin 1, it will not turn it off.
See the installation manual, which is findable by a simple Google/Bing search, page D-1, figure D-1, Note 3.


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Is there any good database for aircraft technical specifications?
Due to using them in my application, I am looking for a database(or guide) of aircraft technical specifications. Is there any source for it(preferably free).

Welcome to aviation.SE! This seems like a very broad topic, are you interested in some specific type of aircraft?

@Pondliffe, thank you. I am interested all kind of active aircraft. I try to create a quick guide for users who are interested in finding proper aircraft according to their demands.

What kind of technical specifications are you looking for? Manufacturer published marketing specifications such as speed and range? Flight operating specifications such as flap and gear speeds or CG range? Maintenance specifications such as brake wear limits?

At the beginning, I would like to have basic specifications such as speed, range, etc. Afterward, It 'd be good to have more details.

One word for the definitive authority on this subject: Jane's.  They'll get you anything you want to know - if the price is right.
Another good source, especially for military aircraft is The Military Analysis Network, run the Federation of American Scientists (FAS).  Great information database and it's free, too!
As with so many other subjects, Wikipedia remains an excellent source of information on aircraft.  It is not a recommended source to cite for writing technical publications of your own, but is a excellent internet portal to additional information and resources e.g. books, periodical articles, etc.

I've always figured Jane's must employ a network of spies and informants to get the data they have. I would look at their diff and think there's no way the military wants this stuff to be public knowledge

+1 for Jane's - the aeronautical engineer's bible! Worth adding the best place to view a copy for free is a university library.

It is worth noting, however, that, while ubiquitous and amazingly thorough, Janes is not something to take at face value.  I worked for a short while at Sikorsky Aircraft doing competitive analysis and typically found that, while they are true, the performance characteristics are either recorded for a vague flight condition, different flight conditions, or something else of the sort.  You have to very careful in order to use Janes and still compare apples to apples.


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How to calculate estimated flight time?
I am trying to calculate estimated flight time accurately. I calculate the distance with the great-circle distance method. I have some specifications of the aircraft such as max speed, cruise speed, stall speed, rate of climb, takeoff over 50ft, takeoff ground run, landing over 50ft, landing ground.
I tried the most straightforward approach(distance/speed), but the result was not nice. How should I calculate the estimated flight time?

Flight time usually doesn't begin until your wheels leave the pavement, I would leave the take off/landing out of it. Your POH should have time to climb charts.

It might help to give some more details here: what aircraft type, what route, and what does "the result was not nice" mean?

I assume that you're a passenger travelling on a flight and you want to know how long the flight will last, from takeoff to landing.
First you would need to get the route you're going to fly. Sometimes the published route is available on flight-tracking sites, for example this one. After that, you can plot the route on an aviation chart to get the distance. If the route is not available, you will need to construct the likely route by guessing which airways the flight will take.
Next you need to figure out your plane's groundspeed. The groundspeed is not constant. When the plane is climbing, part of the engine thrust is directed upwards, so ground speed would be slower. Engine thrust also varies with altitude, so the ground speed will vary throughout the climb. You will need an aircraft performance table, which typically has data at 1000 feet increments. You need to repeat the calculation for each 1000 feet until the aircraft reaches cruise altitude.
We will assume the aircraft remains at a constant cruise altitude for now. You can easily work out the flight time by looking up the cruise groundspeed (not airspeed).
Now we need to figure out when the plane will begin its descend. From the route you obtained earlier, you'd have known the flight's cruise altitude. Flights typically descend 1000 feet per 3 nautical miles. Work your way backwards from the destination, you will have your Top of Descent point. Again, the ground speed will be slower because the velocity vector has a component in the vertical direction. The plane will descend at its cruise airspeed until 10,000 feet, where it will slow to 250 knots.

For a start, this very simplified version would give you a closer estimate to reality. I have left out:

Winds aloft. At high altitude, usually there is a significant wind blowing at one direction. Depending on whether it is head wind or tail wind, it will slow you down or speed you up. Different areas will, obviously, have different wind conditions. Different altitude in the same area will also have different wind conditions.
SIDs and STARs. These are the waypoints which connects flights coming from all directions to a common arrival point for final approach at the destination airport (or the opposite at the departure airport). These waypoints will increase the total length of your route.
Altitude changes. Throughout a flight, the cruise altitude may change. With a new altitude, the engine performance (hence cruise speed) will be different.

In fact, flight time estimation is so complicated that we use software to calculate them. No sane human-being will go through all the data to calculate flight time today.

Note that I did not take into account:

Taxi time: the time it takes to move the aircraft between the gate and the runway on the ground
Holding time: the time which flights are asked to fly in circles near the airport when the airspace is too busy

Your airline will have included these estimates in the quoted time on your flight ticket.

Don't forget time spent dodging nasty weather!


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What does "maximum update interval" mean for Mode S GICB registers?
Transponders have registers for Mode S data and configuration. These registers are updated periodically to provide Mode S services such as ADS-B Airborne Position squitter.
DO-260B and similar documents have Register Allocation Tables that states maximum update intervals for each register(if applicable).
But there is also a register timeout mechanism that states "if a register can not be updated within twice the maximum update interval, it shall be zeroized".
So, what happens if certain register is updated at every (1.5 * maxUpdateInterval) ? Are these maximum update times mere suggestions or is there another rule that forces us to update registers at most maximum update interval?

If you update the register, the values will be set to the values provided.
From that moment, a timer starts running. When the timer reaches 2 * maxUpdateInterval, the register will be set to all zero.
If a radar extracts the register before the 2 * maxUpdateInterval is reached, it will get the values provided at the update. If it will extract the register after 2 * maxUpdateInterval is reached, it will get all zeros in the reply.
For ADS-B, transmission of the register is inhibited (IIRC) when the register is set to all zeros.

I am quoting the DO-260B exactly below( appendix A, page A-53).                      "The ADS-B transmitting subsystem will clear all 56 bits of the Airborne Velocity message if no data is received within 2.6 seconds of the previous input data update."                               The maximum update interval table says 1.3 s is the m.u.i. of Airborne Velocity register.

The minimum update interval and the timeout is there to avoid broadcasting "stale" data which can be misleading. You also have to consider that the update rate is primarily driven by the source of the data.
Most older nav systems (TSO C-129 GPS or FMS) output velocity data once per second, so the standard has to accommodate these systems. The 1.3 sec m.u.i. is there to allow for jitter in the data rate. The 2.6 sec timeout allows you to keep broadcasting in the case where a single data word is lost or corrupted in transmission.
If the update interval goes beyond the 2.6 sec, the register is cleared to avoid broadcasting the "stale" data.  The reality is you wouldn't see a system that regularly updates at 1.5 x m.u.i.

Do you mean i shall send last valid data between 1.3 and 2.6 second time mark( in case data starts to come as invalid).

Populating the GICB registers and transmitting data out of the registers are independent functions. The population function fills each register and starts a timer. The timer will reset every time the data updates.  IF the timer gets to the timeout (2.6 sec in this case), it zeroizes the register.  The transmit side doesn't care what the population side is doing. When a GICB request comes in or the ADS-B squitter is triggered, they grab whatever is in the register. The 1.3 sec is a normal design function. Nothing happens if you go past it until you get to the 2.6 sec limit.


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Will 1090 Mhz band become too congested in the future?
1090 Mhz is currently used for SSR Mode A/C replies and Mode S communication(ELS-EHS replies and ADS-B broadcasts) by civilian aircraft and some of military IFF modes.
With the infamous 2020 ADS-B Mandate about ADS-B usage in certain airspaces(Mandate) , it is expected that this frequency will be very crowded in future.
There are certain methods/precautions to prevent congestion like randomized broadcast timing(between 0.4 s and 0.6 s for Airborne Position for example). F.R.U.I.T. and garble problems are also not new to this frequency.
Are there any discussions in the aviation circles about precautions in anticipation to congested 1090 Mhz band for certain airspaces?

There are some areas where the 1090 MHz frequency is already very busy. The area around Frankfurt am Main in Germany and the Los Angeles Basin airspace is the USA are the most congested in the world.
The direct of impact of ADS-B is an increase in the frequency use of 1090 MHz. At the same time it allows a reduction of number of Mode-S radars, it enables the development of a more effective TCAS with reduced interrogation rates (known as ACAS X), and it reduces the number of interrogations needed by WAM systems. On the long term the impact of ADS-B will likely be positive.
But with the increase in number of flights the 1090 MHz congestion will remain a concern.
There are many discussions in the ATC surveillance circles about the topic and the 1090 MHz frequency (and 1030 MHz as well) is are frequently monitored. There are ground based monitors and periodically there are measurement flights to identify areas of high frequency load. Adding new radars to already congested areas is made very difficult by spectrum protection regulations, instead cross-border surveillance data sharing is encouraged. Some countries monitor 1090 MHz transmissions around the clock and the are plans to have a permanent monitoring service of 1030 MHz and 1090 MHz across Europe that will analyse spectrum usages trends and identify rogue transmission.

Do you mean SSR by "Mode S Radar" or is there a dedicated Mode S Radar? Also I have read somewhere that transponders are designed to reply to hundreds(if not thousands) Mode A/C interrogations. Also , I read from wikipedia that one method of reducing garble is increasing interrogation rate(of mode a/c). Do you have information about estimated percentages of Mode A/C communication compared to Mode S communication?

I meant Mode S specific because they are used to downlink information that is included in the ADS-B messages. Reduction of SSR's in general is also possible but then all Mode A/C only transponders need to be phase out. Mode A/C is using a lot of the capacity on 1090MHz and I'd be glad to see it disappear. Increasing de Mode A/C interrogation rate will increase garbling and fruit. The problem with Mode A/C is the high interrogation repetition rate combined with an often wide radar beam. Aircraft manage to reply to 15 successive interrogations sometimes which is polluting the frequency.

@DeltaLima, do you have more information about rogue transmission?

The FAA was so concerned about ADS-B causing congestion on 1090 that they implemented an entire second data link (978/UAT) and all of the relay complexity that entailed just to mitigate that.  Other countries are free to do the same, and it would be easier for them now since there's a working example to copy, but so far none have.


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Could the Grumman G-21 Goose be started by punching the instruments?
In the 1985 movie "Commando", John Matrix (played by Arnold Schwarzenegger) initiates engine ignition simply by punching the cockpit dials after several failed standard attempts.
Could this ever result in the engines starting in reality?

My old grandmother used to say: Anything mechanical, give it a good bashin.

No, punching would not cause engines to start because you'd need to hold the starter button down (or twist the key depending on the airplane) until the engine catches. It's possible that if there was bad wiring on the panel that punching it could make it work again, but that would likely be temporary.
It's just Hollywood.

Reminds me of "Armageddon" and the russian on the old space-station. But hey, who of us didn't punched a device with a loose connection, at least their is a minimal chance to get it running for some time. The bad side of punching is, over time you could just make the loose connection worse and damage more.

Armageddon - horrible movie. The rest of that scene in Commando isn't any better, the pilot is taking off but doesn't look like she's going to clear the ships on the other side of the harbor when Matrix suddenly pushes the throttles further forward and they just make it. Like the throttles wouldn't have been already maxed!

It's Hollywood. I hope the new Star Trek XIII isn't like the last one, my brain still hurts from the unlogical story ):(

In Star Trek it's 'Illogical'.

Star Wars is illogical. We have an excuse for everything, heisenberg-compensator ;)

It has its own name - Percussive Maintenence.

Hey, it worked on the Millenium Falcon!


text:
Do icing limits exist for parked aircraft?
Are there any aircraft that have a limit on the amount of ice or snow that can be on the aircraft when stationary and on the ground?

I'm not aware of any limits every being published on transport airplanes.  On large aircraft, it's not too big a deal structurally because the bending loads imposed by a snow cover are not significant, since bending load applied by a couple of feet of snow (which weighs about 40lb/sqft) on such a large structure, designed to support 100+ lbs/sqft, is relatively mild.
On little airplanes, this can be a problem however.  Let 2 feet of snow, or 40 lbs/sqft, accumulate on a light aircraft or ultralight with large wings, designed to support maybe 5-15 lbs/sqft of negative load, and you will likely find the wing outboard of the strut is permanently bent down or has collapsed when you want to go flying.  Nature's just done a static load test on your wings and got carried away.
On a metal airplane, you at least take comfort in the fact that if the wing is not permanently bent down after you remove the snow, you're good to go.
On an airplane with wood spars, this is more of a gamble, because wood structures that are overloaded beyond the compression limit of the side in compression (the spar below the strut attachment bolt in the case of snow load) without overloading beyond the tension limit of the side in tension (above the strut attachment bolt, where it just breaks), can suffer from a dormant compression failure in the wood itself.
Compression failures are where the cellular structure of the wood fibres partially collapses.  This can leave the wood apparently undamaged (unless you can inspect the area to detect the tell-tale fine line across the grain), but weaken the wood in tension.  So when you go flying, and the wood below the spar attachment is loaded in tension again and has lost some fraction of its ultimate tensile strength, and you hit a bump that applies some extra G, whoops!
Anyway, if you own a light aircraft with wood spars you need to be aware of this and be extra vigilant about preventing large snow loads on the wings.  I'm not really keen on wood spars on light planes for this reason.  It's a reason you never buy a used Classic with wood spars that's had a wing tip repair (from the tip hitting the ground during a groundloop).  A friend bought an Aeronca Champ once and found his right wing had a wood compression failure above the spar bolt, caused by a wing tip strike, when he took it apart to recover it, after flying it about a year.  He was lucky; any significant negative G in that condition would have been fatal.
You could work out a limit for yourself if you know the wing loading and structural G limit for your own airplane. So if your wing loading at gross is 10 lb/sqft, and it's good for negative 2 Gs in flight, you can estimate that the wing can tolerate 20 lbs/sqft of snow accumulation, or about 1 foot thick and wouldn't want too much more than that to accumulate.

I've seen a Boeing 727 parked at an air museum that tipped over so that the rear fuselage was on the ground, due to the aircraft being heavily covered with ice.  Presumably it would be desirable to avoid that event in an operational aircraft-- to avoid cosmetic damage to the bottom of the rear fuselage if for no other reason.

For transport category airplanes, there are often manufacturer recommendations for storage of aircraft, and engines. The level of storage (length of time and environment) would determine what precautions are recommended.  In the case of transport aircraft I don't know if those requirements are part of the approved maintenance program or not. Standards for maintenance requirements are developed at the industry level by Maintenance Steering Group -3.

No, However to protect airplane from icing , it is recommended to park in closed hanger and the geographical area where icing occurs frequently they keep airplanes batteries always for charted state so that it is easy to take the plane for flying after normal preflight procedure.


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When and where are anti-ice required for supersonic flight?
Many aircraft have heating devices to prevent dangerous icing.  Supersonic aircraft rapidly compress the air, leading to elevated temperatures.  Concorde and Tu-144 used fuel as a heat sink.
How fast do you need to fly so that heating makes anti-ice irrelevant?  How does it depend on the part of the aircraft?  Presumably the leading edge is the first part to warm up without anti-ice.  Are icing conditions different at typical supercruise altitudes?  Is there meaningful water up there?

How fast do you need to fly so that heating makes anti-ice irrelevant?

The True Air Temperature (TAT) that the aircraft's skin will feel can be calculated from the Static Air Temperature (SAT) and the Mach number:
$$ \frac{\text{TAT}}{\text{SAT}} = 1 + \frac{\gamma - 1}{2} M^2 = 1 + \frac{1}{5} M^2 $$
(using $ \gamma = 1.4 $ for air). The SAT does not usually go below -56.5°C in the International Standard Atmosphere, which is the usual temperature in the lower stratosphere (where most supersonic aircraft fly).

At Mach numbers above $ \sim 1.24 $ the resulting TAT will be above 10°C, which is usually defined as the upper temperature, where icing conditions exist.

How does it depend on the part of the aircraft? Presumably the leading edge is the first part to warm up without anti-ice.

Yes, the leading edges would warm up most, but they are also the only part of the aircraft that could possibly accumulate ice. Aircraft that are certified for flight into known icing conditions typically have de-icing or anti-icing systems on the engine inlets, the propellers and the leading edges of the wings, vertical and horizontal stabilizer. But not all aircraft have these systems on all of these surfaces because they are not all affected equally. See e.g. these questions:

Why do only some aircraft require tail anti-icing?
Why are some parts of the wings not protected by the wing anti-ice system in the B737?

Are icing conditions different at typical supercruise altitudes? Is there meaningful water up there?

Humidity is usually quite low in the stratosphere, meaning icing isn't typically a problem here anyway:

The stratospheric air
masses sampled are dry, as expected, having mean
relative humidity over water of 12% and over ice of
23%, respectively. However, 2% of the stratospheric
data indicate ice supersaturation.

(A distribution law for relative humidity in the upper troposphere
and lower stratosphere derived from three years
of MOZAIC measurements)
Most weather phenomena only occur in the troposphere, which means you fly above the weather (although thunderstorm can push clouds to extreme altitudes).


text:
What daily commercial flight is the oldest / has been running the longest?
Out of curiosity, what flight, currently still operating, has the earliest inception?
There are several ways to define this, and I expect available information will determine what definition is most useful. As an example, if a flight's inception date is the earliest date such that there has been a commercial flight on every day (or every week) between that date and today, what flight has the earliest inception date?
Also interested in a flight using the same aerodromes, or with the same airline, or even aircraft type.

It is probably a KLM flight, as KLM is the oldest airline in operation, having been established in 1919 and starting scheduled services in 1921. The hard part is the every day/week part, flights are very seasonal and may skip weeks in slow seasons to certain destinations.

I'm guessing the Second World War would have broken the services though.

In addition of the drastic constraints of the question, after the 2010 volcanic eruption all flights in a part of Europe have been broken, and in the US it has been the same after 9/11. The answer will have little significance.

Qantas also grounded its fleet in 2011, probably ruling any of its flights out of contention. But I think the problem restricted to flights of any airline between the same airport is still interesting.

Related: Oldest airline with the oldest air route - jetphotos.net

"there has been a commercial flight on every day (or every week) between that date and today": How can you know that a scheduled flight was never disrupted one day by a strike, by weather, by a diversion, etc? So how can one even be sure their answer is valid?

I'm open to the answerer limiting the scope of the question. It's hard to know precisely what question to ask when you don't know how detailed available records are.

You could look into the oldest route operated between 2 city pairs by an Airline and then you would end up at the AMS-LHR route by KLM which started service on 19 May 1920 according to Wikipedia. For the USA a lot of airlines have merged together so they would all be left out.

According to the Georgia Encyclopedia one of the oldest flights operated by Delta was Love Field, Dallas to Birmingham, Alabama from 1929 up to 2000. Birmingham ist still served by Delta, but not from Love Field.
According to this the first flight from London to Schiphol was in May 1920. This route ist still in operation by KLM. But London at the time meant Croydon Airport.
On 27 May 1936 Aer Lingus made its first flight from Dublin to Bristol, while the route is also still in operation, the airfields changed. (wikipedia)
Take your pick.


text:
If cleared to cross a runway and expedite but are slow to get away, are you obliged to stop?
Suppose ATC says "Big Jet, cleared to cross runway 36, expedite" and you acknowledge "Cross runway 36, wilco, Big Jet". As you start to move forward  you immediately realize that you are unable to go as quickly as you expected (perhaps there's an incline or a gust of wind -- I'm not sure what's plausible). At the point you realize this, you can still hold short the runway. Are you obliged to stop and reply 'unable' or is that ill-advised?

Just to nitpick...you are never "cleared" to cross a runway, since that is an instruction, not a clearance. So the phraseology used would be "Cross runway 36", not "Cleared to cross runway 36". There's a number of reasons for this, one of them being that hearing "cleared" and "runway 36" in the same sentence can result in some unlucky associations (pilot thinking he is cleared for takeoff etc.)

If you feel you cannot safely comply with any ATC instruction, you can simply reply “Unable” and the controllers will amend your clearance.  Remember: you are pilot in command; you are the final authority on the operation of that aircraft.
So the scenario might play out as:
ATC: “Bigjet, cleared to cross Runway 36.  Expedite crossing and report clear.”
Bigjet: “Cross runway 36 and report clear, Bigjet.”
Bigjet: “So-And-So Ground, Bigjet, Unable.  I’ve got a problem here.”
ATC:  “Bigjet roger hold short of Runway 36 for arriving traffic.  Will you be able to taxi after traffic clears the active?”

If you don't think you can safely comply with an instruction, don't comply with it. If you can remain short of the "hold short" line, stop there and inform ATC. If you have already crossed the line call tower and say "crossed hold short, unable to expedite" or something to that effect so they can have landing traffic go around.
Its been said quite a few times, the pilot is in control of the plane, not ATC. You can agree to something and then later realize you can't comply, that is fine, as long as you communicate with ATC.

Per Part 91, You are cleared to cross until/unless another clearance is obtained. https://www.law.cornell.edu/cfr/text/14/91.123


text:
Do any manufacturers have plans to use turbojets in future aircraft? What is the state-of-the-art in turbojet design?
Turbojets have largely been superseded by turbofans (or turboprops for low-speed flight). Are there any aircraft being planned that would use turbojets?  I'm also interested whether there has been any improvement in turbojet design over the last few decades.

Technically the turbofan is an improvement of the turbojet design. Maybe THE improvement.

The first jets were turbojets simply because the turbine could only support its own compressor. They kept an edge for supersonic flight and will be the engine of choice if we ever design another Mach 3+ aircraft. Also, micro jets for cruise missiles and model aircraft turbines are turbojets to keep them simple. However, the analysis of modern jet warfare showed that the overwhelming majority of flight time is spent at high subsonic speeds, and there a turbofan makes more sense.
Now all modern combat jet aircraft use turbofans, even though their bypass ratio is rather low (around 0.5).
Commercial jet transport engines are solidly turbofans since half a century and have slowly increased their bypass ratio to about 9, less for smaller engines. Now three-spool engines or geared turbofans are state of the art, because they allow more freedom in optimizing the rotation speed of the different sections inside the engine.
Turbojets have benefited from better, more heat-resistant materials and airfoils for turbo machinery just as much as turbofans, but modern designs are overwhelmingly turbofans, so turbojets generally represent a much earlier technological level. To give you an example: The first turbojet used in operation, the Jumo 004, had a mass of more than 700 kg and produced 8.8 kN of thrust. The engine of the Eurofighter, the EJ200, is only slightly bigger in mass and has similar dimensions, weighing 990 kg, but produces seven times the thrust of the Jumo 004. With reheat, thrust is more than 10 times that of the Jumo 004, which had no afterburner. The pressure ratio could be increased from 3.2 to 26 (that is the progress in compressor aerodynamics), and the turbine entry temperature from 840°K to 1800°K (that is the progress in materials).

Aren't turbojets actually the most efficient engines in about the mach 2-3 range, with ramjets surpassing them above mach 3 or so?

@Sean: Their efficiency at that speed is mostly the efficiency of the intake. The engine's task is to swallow the air coming from the intake and to accelerate it as much as possible. This needs rather simple compressors since the pressure at the engine face is already so high. Turbojets are nothing without their intake at Mach 3.

Maybe this helps, although from 2013
"Superjet" variable cycle jet engine could power future fighter aircraft
http://www.gizmag.com/ge-aviation-develop-advent-variable-cycle-jet-engine/25556/


text:
Could some one explain me with the mathematical relations on how the double bubble fuselage cross section (example A380) is designed.

Could some one explain me with the mathematical relations on how the double bubble fuselage cross section (example A380) is designed.

There is no double bubble for the A380, this is an ellipse Comparison of cross sections.

Mathematical "relations" of what exactly?

I have no idea what the captions in that diagram are supposed to mean. "Abreast" means "next to each other" so, while the 777 diagram does indeed show nine-abreast seating, none of the others shows more than ten-abreast.

@DavidRicherby: It's apparently the sum of all bridges.

A380 actually has an elliptical cross section, not double bubble. 'Double bubble' fuselage cross sections (also called double lobe) are usually used in case of aircraft which require specific arrangements for carrying passengers/cargo and in which case using a circular or elliptical fuselage would result in a large wastage of space or because this type of arrangement is cheaper to make. Another reason for this appearance is that some aircraft were extensively modified (for reasons other than the original intentions) resulting in this shape.
The double lobe fuselage aims to reduce the wasted space by having fuselage in two intersecting circles, joined together at the floor. The (relative) size of the circles is determined by the requirements. A good example is the Boeing C-97 Stratofreighter, which was a military transport based on B-29 Superfortress.
Boeing notes:

... it had a double-lobe fuselage consisting of two intersecting circular sections, so that the 74-foot-long (23-meter-long) upper deck had a larger diameter.

Image from Boeing.com
The civilian counterpart of the C-97, the Boeing 377 Stratocruiser inherited this shape having a double lobed structure, with 100 passengers on the main deck plus 14 in the lower deck lounge.

Boeing 377 Stratocruiser fuselage cross section; image from tdpri.com
These aircraft were later modified to carry oversized aircraft parts as the Pregnant Guppy, Super Guppy and Mini Guppy, all having the distinctive double lobed design.
Note that most of the double bubble aircraft are for carrying cargo. Contemporary aircraft with a similar arrangement include the Airbus Beluga which again are used for transporting oversized aircraft parts.

Airbus beluga, image from australianaviation.com.au
The Beluga is an example of how specialized requirements required this design. This aircraft was designed because none of the available large transports had enough space to transport the required sub-assemblies. Designing and building a new aircraft for carrying these sub-assemblies (including fuselage sections) would have been prohibitive (only five were made); so Airbus modified an existing aircraft according to requirements.
Another aircraft that acquired this shape as a result of modifications was the Hawker Siddeley Nimrod, which had this shape due the addition of a bottom section to the De Havilland Comet. The lower section had the radar, bomb bay etc, while the upper section had the crew.
Quite a few airliners have utilized this shape in the past, though the shape is not as pronounced. Airline manufacturers, from Boeing to Douglas used them as they are efficient in using space. For example, the Boeing 707 fuselage cross section below shows this design.

707 fuselage cross section; image from forum.justflight.com
Also, as I noted before, the A380 has an elliptical cross section, not double bubble.

I think the biggest rationale of double lobe is when you add another bubble to an existing hull, as in C97 and 377 repurposing B-29's design. 747 is a notable example, however from the very beginning the hump was designed to not take entire length of the hull, hence here too it was easier to design single lobe hull first, and the slap on the second one as necessary.

I don't know the mathematical relations, but some general remarks:

Both circles are matched at the cargo roof - passenger floor intersection, as this is the most efficient place to transfer the loads. This determines the point at which both semi-circles start/end.
In the A380 it's hard to see it, but here is a clearer example

Source

The size of the lower semi-circle is dictated by the cargo container dimensions. You want to make it tall enough to fit the targeted container.
The size of the upper semi-circle is dictated by passenger-space-requirements. You want to have enough space such that your passengers can comfortably sit/walk/anything else they do during their journey.


text:
Could Sudden Decompression Cause You to be Shot Out of the Tunnel on a B-29?
One of the features of the WWII B-29 bomber was that it was pressurized. The aircraft had pressurized areas in the front and the back of the aircraft. Connecting the two was a pressurized tunnel over the bomb bay, shown below.

This tunnel was a popular resting place for crew during long missions because they could stretch out in it. (Despite what some early pictures show, the B-29s used in the war did not have bunk beds.)
However, many crewmen thought that resting in the tunnel was also a bit risky because, if the plane suddenly lost pressure in either the front or rear compartment, they could have been shot out of the tunnel at considerable speed.
Was this a valid concern?
For purposes of this example, assume that the tunnel was 2 feet in diameter and 35 feet long, that they were flying at 25,000 feet (pressurized to 6,000 feet) and that the crewman weighed 150 pounds and was blocking about 1/2 of the cross-section of the tunnel.

If lying down, probably air would just whoosh past you for a second or two until equalized and it might slide you along a bit.  There isn't a lot of volume in the two pressure chambers and a decompression would have to be instantaneous and massive (like a waist gunner blister blowing out), and the whoosh of air would be quite brief.
However, it'd be worse if you were on your hands and knees. You'd get carried along and knocked down for sure for at least a short distance, and if you were near the end on your hands and knees, you might come spilling out with enough velocity to get banged up a bit.  So I would be wary of a decompression while climbing in and out and crawling along on all fours, but once laying flat I don't see that sort of thing happening.

Now, if you had a 75 inch waistline from eating too many mission debrief doughnuts (and somehow still were fit to be a crewman) so you were a tight fit, you probably would come shooting out the end, since you are basically a human air rifle pellet with nearly 3000 lbs (6.6 psi) trying to get past you.

So the guy in the picture might have been taken for a bit of a ride?

He'd be knocked over and might slide a long a bit, but the cabin volume isn't that big for  a very long whoosh of air and there's enough space around him for it to escape.

It sounds possible. There was an accident where a navigator was sucked up and out of the astrodome on a Constellation while taking a star sight with a sextant after the dome shattered. See https://en.wikipedia.org/wiki/List_of_accidents_and_incidents_involving_the_Lockheed_Constellation and https://en.wikipedia.org/wiki/Astrodome_(aeronautics).

That sounds horrible! For awhile, the B-29s had a problem with the rear side-domes cracking or blowing out. This was concerning enough that some gunners wore straps connected to the airplane. One gunner was actually blown entirely out of the aircraft and was saved by his strap. This must have been fixed because I am not aware of anyone who died from this problem. And I don't recall talking to any gunners who wore a strap in 1945..

There is a photo of that guy hanging out the waist blister hole.   The opening is quite large and you are leaning right into it when using the sighting tiller, so it wouldn't take much to blow you out. The Connie navigator would've been a tighter fit in the astrodome hole, so that would be comparable to my joke about the guy with the 75 inch waist in the B-29's tunnel.


text:
What does the preliminary report on the Ethiopian B737 MAX accident show?
In early April the Aircraft Accident Investigation Bureau of Ethiopia released a preliminary report on the crash of Ethiopian Airlines flight 302 that happened on March 10, 2019.  There apparently is some technical detail in it from the "black boxes".  What are some of the main technical things the report shows about the flight?

In the short summary, the preliminary report (33-page PDF available here) gives these details:

Shortly after takeoff, the Angle of Attack sensor recorded value became erroneous and the left stick shaker activated and remained active until near the end of the flight. In addition, the airspeed and altitude values from the left air data system began deviating from the corresponding right side values.

Among the few initial findings, the preliminary report has these:

Shortly after liftoff, the value of the left angle of attack sensor deviated from the right one and reached 74.5 degrees while the right angle of attack sensor value was 15.3 degrees; then after, the [left] stick shaker activated and remained active until near the end of the flight.
After the autopilot disengaged, the [Flight Data Recorder] recorded an automatic aircraft nose down (AND) trim command four times without pilot’s input. As a result, three motions of the stabilizer trim were recorded. The FDR data also indicated that the crew utilized the electric manual trim to counter the automatic AND input.

In the section giving details derived from the Flight Data Recorder and Cockpit Voice Recorder, the following items are included:

At 05:40:00 shortly after the autopilot disengaged, the FDR recorded an automatic aircraft nose
  down (AND) activated for 9.0 seconds and pitch trim moved from 4.60 to 2.1 units. The climb was
  arrested and the aircraft descended slightly.
At 05:40:03 Ground Proximity Warning System (GPWS) “DON’T SINK” alerts occurred.
The column moved aft and a positive climb was re-established during the automatic AND motion.
At 05:40:12, approximately three seconds after AND stabilizer motion ends, electric trim (from
  pilot activated switches on the yoke) in the Aircraft nose up (ANU) direction is recorded on the
  DFDR and the stabilizer moved in the ANU direction to 2.4 units.

A second similar sequence (automatic nose down trim, “DON’T SINK” from GPWS, and pilot-commanded electric nose up trim) then occurred from 05:40:20, to 05:40:28.
The diagram below, from a report appendix, shows aircraft pitch related data from the FDR from the first automatic nose-down to the end of the recording.  (Time advances from left to right.)

At 05:40:35, the First-Officer called out “stab trim cut-out” two times. Captain agreed and FirstOfficer confirmed stab trim cut-out.
At 05:40:41, approximately five seconds after the end of the ANU stabilizer motion, a third instance
  of AND automatic trim command occurred without any corresponding motion of the stabilizer,
  which is consistent with the stabilizer trim cutout switches were in the "cutout" position.
From 05:40:42 to 05:43:11 (about two and a half minutes), the stabilizer position gradually moved
  in the AND direction from 2.3 units to 2.1 units. During this time, aft force was applied to the
  control columns which remained aft of neutral position. The left indicated airspeed increased from
  approximately 305 kt to approximately 340 kt (VMO). The right indicated airspeed was
  approximately 20-25 kt higher than the left.
At 05:41:46, the Captain asked the First-Officer if the trim is functional. The First-Officer has replied
  that the trim was not working and asked if he could try it manually. The Captain told him to try.
At 05:41:54, the First-Officer replied that it is not working.
At 05:43:11, about 32 seconds before the end of the recording, at approximately 13,400 ft, two
  momentary manual electric trim inputs are recorded in the ANU direction. The stabilizer moved in
  the ANU direction from 2.1 units to 2.3 units.
At 05:43:20, approximately five seconds after the last manual electric trim input, an AND automatic
  trim command occurred and the stabilizer moved in the AND direction from 2.3 to 1.0 unit in
  approximately 5 seconds. The aircraft began pitching nose down. Additional simultaneous aft
  column force was applied, but the nose down pitch continues, eventually reaching 40° nose down.
  The stabilizer position varied between 1.1 and 0.8 units for the remainder of the recording.
The left Indicated Airspeed increased, eventually reaching approximately 458 kts and the right
  Indicated Airspeed reached 500 kts at the end of the recording.

The "automatic aircraft nose down" events mentioned in the above can be ascribed to the MCAS (Maneuvering Characteristics Augmentation System), which Boeing only started informing pilots about in late November, 2018.

Commentary at Seattle Times